The operating frequencies of integrated circuits such as memory devices are progressively increasing. To take advantage of these high frequencies computing systems are designed to transmit signals along their busses and between system components at comparable frequencies.
Some difficulties may be encountered when transmitting and receiving data between system components (e.g., between integrated circuits) at high frequencies. Buses behave like transmission lines, where impedance mismatches lead to signal reflection and interference effects. Termination resistance can be used to maintain signal quality over interconnections by matching impedances to minimize signal reflections.
Conventional memory systems, such as double data rate (DDR) dynamic random access memory devices (DRAMs) typically have multi-drop bus architectures that are terminated with a resistor that is resident on the motherboard. In other conventional memory systems, the termination resistor is resident on the integrated circuit.
The term “on-die termination (ODT)” refers to a termination resistor that is resident on the integrated circuit. The value of ODT is set when a computing system is initialized. After initialization, the ODT can be activated or deactivated with the value that is set during initialization.